As is generally known, an objective within the scope of the development of internal combustion engines is to lower their fuel consumption. For this purpose, when it comes to the drive of motor vehicles, a so-called hybrid drive, for example, is employed, which comprises an internal combustion engine as well as an electric motor, whereby the internal combustion engine drives the electric motor that functions as a generator, so that an electric storage unit can be charged. Moreover, so-called start-stop systems are used, with which the internal combustion engine is switched off when the vehicle is standing still. In these two configurations, which are given by way of an example, a scenario can occur in which the internal combustion engine is at first operating at a high load and then abruptly turned off, for example, when the electric storage unit of a hybrid drive is sufficiently charged or, in the case of a start-stop system, when the vehicle is braked from full speed all the way to a standstill. In actual practice, aside from the mechanically driven coolant pumps, there are also electrically driven coolant pumps for such situations, so that the coolant is kept circulating and an impermissible rise in the temperature of the coolant is prevented, which would occur due to the considerable heat capacity of the housing of the internal combustion engine. A drawback is that two units are needed here. It is likewise a disadvantage that the purely mechanically driven ancillary units of an internal combustion engine such as, for instance, a coolant pump, always increase the fuel consumption of the internal combustion engine since they convey coolant even when this is not necessary, for example, at the time of a cold start of the internal combustion engine.
In order to avoid these inadequacies, the German translation of a European patent specification, DE112009000861 T5, for example, discloses a coolant pump having the features described as follows. This coolant pump has an impeller that is arranged on an impeller shaft. This coolant pump has a drive device for the impeller, whereby the drive device has a mechanical drive and an electric motor drive. In this context, the pump impeller shaft is divided into a driving section and a driven section whereby a coupling that can be opened and closed is installed between the driving section and the driven section. Several switching states can be established by means of this coolant pump. For example, the coupling can be closed so that the coolant pump is driven purely mechanically. Moreover, the mechanical drive can be interrupted by opening the coupling, so that, when the electric motor is not being operated by the engine, no coolant is being conveyed, thus, for instance, shortening the warm-up phase of the internal combustion engine. Moreover, when the coupling is opened, only the electric motor can be operated so that, in the case of a sudden standstill, coolant can still be conveyed, as described above. A disadvantage of the ancillary unit according to DE112009000861 T5 is that the coupling installed between the driving section and the driven section requires an additional actuator such as, for example, an electromagnet with a coil, a measure that not only calls for additional components but also has a detrimental effect on the installation size of this ancillary unit.